The present invention relates generally to hot water heaters and more particularly to near boiling hot water heaters.
Hot water dispensers that mount to sinks are common. Such dispensers consist of two main parts, a water tank with a heater and a faucet. In the water tank water is heated by the heater and stored until needed. The tank and associated plumbing are usually installed below the sink where they are out of the view of the user. The faucet is usually mounted above the sink such that a user can dispense the amount of hot water desired while any excess hot water falls harmlessly into the sink. Such dispensers are typically used by opening a valve on the faucet to dispense the hot water stored in the tank to the user who can then enjoy, for example, a hot cup of soup, hot chocolate, or tea. Several different methods may be used to open the valve such as twisting a handle, depressing a lever, or pushing a button on the faucet.
A typical prior art hot water dispenser, such as the In-Sink-Erator, Instant Hot(trademark), hot water dispenser, model number H-990-W-5, is shown in FIG. 1. Such prior art hot water dispensers 10 are typically mounted such that the water tank 12, with the heater 18, is attached to a wall beneath the sink by well known means. The faucet 34, with the activating valve 32, is typically attached to the upper surface of the sink through a hole in the sink cabinet""s upper surface and is oriented such that any water emanating from the faucet will fall into the sink and drain away. Tubing 20, 26, 28, and 30, typically copper, stainless steel, or plastic, connects the faucet 34 with the tank 12. Tubing 28 allows hot water 16 in the tank 12 to flow to faucet 34. Tube 30 is connected to a water supply by any suitable means known in the plumbing arts. Prior art hot water dispensers typically heat the dispensed water 16 to a temperature below boiling, typically between 180xc2x0 F. and 190xc2x0 F.
Tank 12 is made of any suitable material such as stainless steel, copper, or high temperature plastic that can hold the heated water 16 in the tank. The water 16 in the tank 12 is heated by heating element 18. Heating element 18, in the prior art, is typically a 750-watt electric heating element that is regulated by a temperature adjustable thermostat 14 (electrical connection not shown).
A fixed baffle 22 divides the tank 12 into a hot water storage area 40 and an expansion area 24. Tube 26 acts as a vent for expansion area 24 so that neither low pressure nor high pressure will be created to restrict the flow of water into and out of expansion area 24. The baffle 22 is a rigid or semi-rigid material, such as stainless steel, copper or heat resistant plastic to which venturi 38 may be attached. The expansion area allows for any water remaining in tube 28 after water flow into the tank is shut off through tube 20 to drain into the expansion area through hole 42. Additionally, because the cool water that has replaced the water used expands by about 8 percent as it is heated, an expansion area must be provided or water will be forced out of tube 28 where it would drip from faucet 34. Consequently the heated and expanded water flows into venturi 38 through hole 42 and into expansion area 24. The venturi 38 is affixed about the lower end of tube 28. As water is forced out of tube 28 venturi 38 creates low pressure at opening 42 as water in tube 28 flows past it. The low pressure draws water from expansion area 24 through the opening thus draining any accumulated water in expansion area 24.
In order to dispense hot water 16, the user activates a spring-loaded, twist-actuated valve 32, although any type of on-off water valve may be used, to allow cold water in tube 30 to flow into tube 20. Tube 20 is connected to the bottom of tank 16 at inlet 36. As relatively cold water enters the tank 12 through inlet 36, hot water is forced out of tank 12 and into dispensing tube 28 and ultimately through faucet 34. Faucet 34, In-Sink-Erator(trademark) model number 41760, amongst other things, constitutes a mounting device for valve 32 and a conduit for various tubes carrying water to and from the tank 12. After an amount of hot water is dispensed in this fashion, the cold water received at inlet 36 is heated in preparation for the next activation of valve 32.
In some applications it is desirable to dispense water hotter than 190xc2x0 F. For example some users can taste the difference between tea that is brewed using water at 190xc2x0 F. versus water that is near boiling (e.g., 205xc2x0 F.-212xc2x0 F.), and these users prefer the latter temperature. Water at near boiling temperatures may be desirable for other reasons as well.
Because of the desire for water at near boiling temperatures, other types of prior art hot water dispensers have been designed that heat the dispensed water to near boiling, and some even flash the water to steam before dispensing the water or steam. These prior art hot water dispensers provide hot water at or above 205xc2x0 F. or may even provide steam for such uses as cappuccino. These types of prior art hot water dispensers provide near boiling hot water by utilizing highly accurate (and consequently expensive) thermostats to continuously cycle the heating element on and off in order to maintain the requisite near boiling water temperature.
These types of near boiling dispenser must contend with the possibility that the heated water may boil and turn into steam, thereby greatly expanding in volume and providing the potential for damaging components and injuring users. While steam generation is desired in some circumstances, the hot water dispenser must be designed to prevent the damaging effects of steam generation. In order to prevent damage from steam generation, typical prior art hot water dispensers typically utilize a pressure relief valve on the tank to prevent overpressure in the tank.
The reader is referred to the following references for further background regarding the design and operation of prior art hot water heaters, which are incorporated herein by reference in their entirety: U.S. Pat. Nos. 6,266,485, 6,256,465, 6,094,524, 6,069,998, 4,513,887, and pending application Ser. No. 09/564,199 filed May 4, 2000.
It has generally been regarded as difficult to design a relatively cheap, reliable, and safe system that can dispense near boiling water. Prior art hot water dispensers that dispense near boiling hot water are expensive to manufacture and operate. In this regard, it should be noted that the heat loss rate of water increases as its temperature increases. In other words, 205xc2x0 F. water cools quicker than water between say 180xc2x0 F. to 190xc2x0 F. Thus the higher temperature water must be reheated more often than cooler water to keep it at the desired temperature, which raises energy costs. To compensate for the increased heat loss rate of higher temperature water, additional insulation can be used around the tank. Of course more insulation leads to higher manufacturing costs. Additionally, because the water is being held at a temperature closer to its boiling point, a more accurate thermometer must be used to avoid overheating the water. Overheating the water could lead to unwanted steam generation and higher tank pressure than the tank is designed to withstand. A more accurate thermometer is expensive, which again leads to higher costs. Additionally, pressure relief or safety valves to protect against the possibility of damage due to steam generation further raise manufacturing costs.
Embodiments of the present invention provide a hot water dispenser capable of heating water to near boiling temperatures (e.g., 205xc2x0 F. to 212xc2x0 F.). When water at near boiling temperatures is required, a secondary heating element is activated. The secondary heating element is thermally coupled to the dispensing tube so that the water in the tube may be further heated as it passes through the dispensing tube from the tank to the dispensing outlet. Heating the water to near boiling just prior to its being dispensed reduces energy costs because the near boiling temperature water is not stored and allowed to cool. Additionally, the need for expensive insulation or expensive thermostats is reduced.